1. Field of the Invention
The present invention relates to a light-transmitting sintered body, light-emitting tube and electric discharge lamp using the same.
2. Prior Art
Sintered bodies represented by ceramics are not transparent and have been considered to be unsuitable as optical materials. In recent years, however, light-transmitting sintered bodies have been developed and used as light-transmitting materials with an excellent heat-resisting properties in such applications as light-emitting tube body, inspection windowpane for high temperature, optical lens, infrared windowpane, substrates for mounting functional devices, high voltage sodium lamps or electronic devices such as the light-emitting tube and the electric discharge lamp, optical memory, optical shutter, scintillator and solid laser.
The light-transmitting sintered bodies that have been known so far include Al2O3 sintered body (Japanese patent application laid open under No. 6-211569), ZnO sintered body (Japanese patent application laid open under No. 55-14757), PLZT sintered body (Japanese patent application laid open under No. 5-139862), Y3Al5O12 sintered body (Japanese patent application laid open under No. 6-107456), M3Al15O12 sintered body (M is at least one element selected from the group consisting of Er, Tm, Ho, Dy, Lu, Tb; Japanese patent application laid open under No. 11-147757), oxide sintered body containing sintered body containing Al100-a Maxe2x80x94obtained by heating in oxygen or atmospheric airxe2x80x94as metallic element in the ceramics (M is one or more elements selected from the group consisting of Y, Ce, Nd, Sm, La, Gd, Pr; Japanese patent application laid open under No. 6-56514), MgAl2O4 sintered body (Japanese patent application laid open under No. 6-171930), AlON sintered body (Japanese patent application laid open under No. 7-309667), AlN sintered body (Japanese patent application laid open under No. 5-120909), cubic BN sintered body (Japanese patent application laid open under No. 5-221730), Si3N4 sintered body (Japanese patent application laid open under No. 5-286766), BaF2 sintered body (Japanese patent application laid open under No. 6-24828), Y2O3 sintered body (Japanese patent application laid open under No. 11-157933), such sintered bodies as aluminum-type oxynitride, hafnium-type oxynitride, zirconium-type oxynitride, titanium-type oxynitride, zirconium-type nitride, hafnium-type nitride (Japanese patent application laid open under No. 9-92206).
In addition, the following light-transmitting sintered bodes are known: SiAlON sintered body, MgO sintered body, BeO sintered body, Gd2 O3 sintered body, CaO sintered body, ThO2 sintered body etc.
Also known are light-transmitting fluorescent in visible or ultraviolet region under an irradiation of ultraviolet light. Among them are Y3Al5O12: Tb3+ (U.S. Pat. No. 3,767,745) and Y2O3: Gd3+ (G. Blasse and B. C. Grambaier; Luminescent Materials, Springer-Verlag, pp. 157-159).
It is understood that the light-transmitting sintered bodies mentioned above include the so-called light-transmitting ceramics.
The above-mentioned light-transmitting sintered bodies are obtained this way: a mixture of sintered body ingredient materials of an aluminum compound, rare earth elements, silicone compound etc. is pressure molded and well sintered by sintering means such as heating.
Furthermore, light-emitting tubes constructed of the above-mentioned light-transmitting sintered bodies and electric discharge lamps and illumination equipment using the light-emitting tubes are known (Japanese patent application laid open under No. 5-266861).
The light-emitting tube formed of the light-transmitting sintered bodies has an enclosure with a pair of electrodes therein which is sealed with inert gas, mercury, halogen gas or the like therein. In the light-emitting tube, a reduced pressure atmosphere or a high pressure atmosphere is maintained. The light-emitting tube made with the above-mentioned light-transmitting sintered bodies is superior to the prior art light-emitting tube made with silicon oxide in heat resistance and corrosion, and permits application of high power. By using the light-emitting tube, therefore, the electric discharge lamp can be raised in luminous flux and illumination equipment can be increased in quantity of light.
In addition, the light-transmitting fluorescent sintered body has a capability to convert ultraviolet rays into visible rays and, it is considered, can be applied as functional light-transmitting sintered body capable of raising the luminous flux emitted from the light-emitting tube by converting into visible rays the ultraviolet rays radiated within the light-emitting tube and capable of controlling the color rendering of the light emitted from the light-emitting tube.
In the prior art, as set forth above, the known materials that can be made into light-transmitting sintered bodies are only the substances with the following compounds as main components: Al2O3, ZnO, Y2O3, PLZT, Y3Al5O12; the above-mentioned M3Al15O12; oxides containing the above-mentioned Al100-a Maxe2x80x94obtained by heating in oxygen or in the atmospheric airxe2x80x94as metallic element in the ceramics; MgAl2O4, AlON, AlN, cubic BN, Si3N4, BaF2; aluminum-type nitride; hafnium-type nitride, zirconium-type nitride, titanium-type nitride, zirconium-type nitride, hafnium-type nitride; SiAlON, MgO, BeO, Gd2O3, CaO, ThO2 etc.
The materials that can be used for the following articles are limited because the purposes of them are different and those articles have to be made with such limited kinds of materials. The articles include a variety of component parts manufactured with light-transmitting sintered bodes such as the light-emitting tube body, inspection windowpane for high temperature, optical lens, infrared windowpane, substrate for mounting functional elements and such electronic devices as the light-emitting tube, electric discharge lamp, optical memory, optical shutter and solid laser.
For this reason, it is impossible to fully meet the performance requirements demanded of those articles, and in addition the manufacturing method and applications are limited.
Furthermore, the light-emitting tubes using the prior art light-transmitting sintered bodies, especially one using Y3Al5O12 light-transmitting sintered body presents this problem: the light emitting material (halide) sealed in the light-emitting tube undertakes a chemical reaction, lowering the light transmittance. And a light-emitting tube of a light-transmitting sintered body has been wanted which is made of a material different from the prior art.
Furthermore, the prior art light-emitting tube that makes up the electric discharge lamp and illumination equipment is formed of a non-fluorescent light-transmitting sintered body of non-fluorescent substance that does not emit light when irradiated with ultraviolet rays with a wave-length of not shorter than 100 nm and not longer than 380 nm. The ultraviolet rays that occur within the light-emitting tube merely radiate out and are not converted into visible rays, and therefore are low in luminous flux. Furthermore, even if a light-emitting tube is constructed with a light-transmitting fluorescent sintered body so that it can convert the ultraviolet rays into visible rays, the kinds of available light-transmitting fluorescent sintered bodies are quite limited in number and there is no suitable fluorescent material to choose, and the fluorescent colors of the light-emitting tube are limited to specific ones. The known light-transmitting fluorescent sintered bodies that emit light when irradiated with ultraviolet rays include only those based on Y3Al5O12:Tb3+ or Y2O3:Gd3+. The light-emitting tube that is made of the light-transmitting fluorescent sintered body has not been put to practical use as general product for manufacturing and other reasons. Y3Al5O12: Tb3+, Y2O3: Gd3+ etc. are relatively low in light emitting efficiency under irradiation with ultraviolet rays with a wave-length range from 140 to 280 nm, especially 147 nm, 185 nm, 254 nm. Even if component parts such as the light-emitting tubes using those light-transmitting fluorescent sintered bodies and a light-emitting tube are formed of a combination of the light-emitting tube body and ultraviolet ray source, or an electric discharge lamp is made using the light-emitting tube, no sufficient light emission is achieved.
For this reason, a light-transmitting fluorescent sintered body has been sought after which is formed of a light-transmitting fluorescent sintered body other than Y3Al5O12: Tb3+, Y2O3: Gd3+ and which emit light with high efficiency under irradiation with ultraviolet rays with a wave-length of 140 to 280 nm.
In view of the disadvantages of the prior art, the inventors conducted intensive researches and found that specific substances other than the above-mentioned substances for the light-transmitting sintered body are suitable for forming a light-transmitting sintered body and a light-transmitting fluorescent sintered body as well. As a result, the present invention has been completed.
Accordingly, it is an object of the present invention to solve the problems with regard to efficiency or performance, uses, manufacturing process in which the prior art light-transmitting sintered bodies have failed and to provide a light-emitting tube using a light-transmitting sintered body and light-transmitting fluorescent sintered body formed of the above-mentioned specific substances and an electric discharge lamp using the same.
To accomplish the foregoing objects, the light-transmitting sintered body according to the present invention is formed as in the following.
That is, the light-transmitting sintered body according to the present invention is formed mainly of a compound having a magnetoplumbite structure or a compound having xcex2-alumina structure except for aluminum oxide if viewed from an angle of the crystal structure. It is understood that hereinafter (II) indicates that the ionic valence is two while (III) indicates that the ionic valence is three.
The compounds having the magnetoplumbite structure or xcex2-alumina structure include the following. (But the presence of the compounds in the form of light-transmitting sintered body is not known.)
(1) Compounds of the chemical formula xcex1xcex4xcex511O19 (oxides; xcex1 represents at least one element selected from the group consisting of Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, In, Tl, Sb, Bi; xcex4 represents at least one element selected from the group consisting of Be, Mg, Mn, Zn; xcex5 represents at least one element selected from the group consisting of B, Al, Ga, Sc, Fe (Japanese patent application laid open under No. 49-77893).
(2) Compounds of the chemical formula xcex3xcex4xcex510O17 (oxides: xcex3 represents at least one element selected from the group consisting of Li, Na, K, Rb, Ca, Sr, Ba, Eu (II), Sm (II), Yb (II), Dy (II), Pb; xcex4 and xcex5 are the same elements as xcex4 and xcex5 of the compounds of the above-mentioned chemical formula xcex1xcex4xcex511O19 (Japanese patent application laid open under No. 49-77893).
(3) Compounds of the chemical formula xcex1xcex4xcex512O18N or xcex3xcex511O16 N(oxynitride; xcex1, xcex3, xcex4, xcex5 represent the same elements as xcex1, xcex3, xcex4, xcex5 in the compounds of the as mentioned above chemical formula xcex1xcex4xcex511O19 or xcex3xcex4xcex510O17 (S. R. Jansen et al., J. Electrochemical So. Vol. 146 (1999) pp. 800-806).
(4) Compounds of the chemical formula xcex3xcex512O19 (oxides: xcex3, xcex5 represent the same elements as xcex3, xcex5 in the compounds of the as mentioned above chemical formula xcex3xcex4xcex510O17) (J. L. Sommerdijk and A. L. N. Stevels, Philips Technical Review, 37 (1977) pp. 221-233 and the related references).
To be more concrete, the following examples are given:
(1) 1.29 (Ba, Ca)O. 6Al2O3: Eu2+ (BAL), BaMgAl10O17: Eu2+ (BAM), BaO.4Al2O3: Eu2+ (BAE), (Ce, Tb) MgAl11O19(CAT) (B. Smets et al., J. Electrochemical Soc. Vol. 1365 (1989) pp. 2119-2123), phosphor such as BaAl11O16N: Eu2+ (Jansen et al., Electrochemical Soc. Vol. 146 (1999) pp. 800-806), BaMgAl10O17: Mn2+, (Ba, Sr) MgAl10O17: Eu2+, (Ba, Sr)MgAl10O17: Mn2+, CeMgAl11O19: Tb3+, CeMgAl11O19: Tb3+, CeMgAl11O19: Mn2+, CeMgAl11O19: Mn2+, CeAl12O18N, Tb3+ (phosphor handbook (Ohm publishing company) pp. 208-210).
(2) Host compounds as host for the above-mentioned phosphor, that is, 1.29 (Ba, Ca)O.6A12O3, BaMgAl10O17, BaO.4A2O3, CeMgAl11O19, BaAl11O16N, (Ba, Sr) MgAl10O17, CeAl12O18N.
(3) Compounds analogous to those (SrMgAl10O17, CaMgAl10O17, MgAl12O19, CaAl12O19, SrAl12O19, EuAl12O19, LaMgAl11O19, PrMgAl11O19, EuMgAl11O19, TbMgAl11O19, GdMgAl11O19, MgAl11O16N, CaAl11O16N, SrAl11O16N, ScAl12O18N, PrAl12O18N, NdAl12O18N, DyAl12O18N, ErAl12O18N etc.)
(4) Compounds in which alkaline earth metallic elements in the above-mentioned phosphor, host compounds, analog compounds are substituted with rare earth elements with an ionic valence of two, alkaline elements or Pb; compounds in which rare earth elements with an ionic valence of three are substituted with In, Tl, Sb, Bi; compounds in which Al is substituted with Ga or Fe.
Compounds having the magnetoplumbite structure or compounds having a crystal structure, that is xcex2-alumina structure except for aluminum oxide are preferably aluminum compounds and furthermore it is desirable that those compounds contain alkaline earth elements (that is, Be, Mg, Ca, Sr, Ba, Ra) as main component. In addition, it is desirable that those compounds are oxides.
However, all the light-transmitting sintered bodies according to the present invention are not compounds having the magnetoplumbite structure or xcex2-alumina structure except for aluminum oxide.
Among the light-transmitting sintered bodies according to the present invention classified according to the component is a sintered body formed mainly of a compound containing rare earth elements with an ionic valence of two, aluminum element and oxygen element as main components. It is understood that the main components are elements that can be the above-mentioned compounds forming the light-transmitting sintered body and do not contain elements forming the so-called sintering auxiliaries.
The following compounds containing rare earth elements with an ionic valence of two, aluminum element and oxygen element as main components may be cited as examples (but as in the above-mentioned case, the presence of the compounds in the form of light-transmitting sintered body is not known). That is, the following compounds may be named:
Phosphor such as BAL, BAM, BAE, BaAl11O16N: Eu2+;
In addition, bivalent rare earth elements ion-activated aluminate-type efficient phosphor activated with bivalent rare earth elements ions that emit fluorescence under irradiation with ultraviolet rays with a wave-length of 253.7 nm such as 2SrO.3Al2O3: Eu2+ (SAL), 4SrO.7Al2O3: Eu2+ (SAE), BaAl2O4: Eu2+, SrAl2O4: Eu2+, Dy3+, CaAl2O4: Eu2+, Nd3+;
Compounds such as Eu(II)Al2O4, Sm(II)Al2O4, Yb(II)Al2O4, Eu(II)4Al14O25, Sm(II)4Al14O25, Yb(II)Al14O25, Eu(II)MgAl10O17, Sm(II)Al12O19, Yb(II)Al11O16N.
The above-mentioned bivalent rare earth elements ion represents at least one rare earth element ion selected from the group consisting of Eu (II), Sm (II), Yb (II), Dy (II).
It is noted that SrAl2O4: Eu2+, Dy3+ and CaAl2O4: Eu2+, Nd3+ bivalent rare earth elements ion activated aluminate-type efficient phosphor have attracted attention in recent years as fluorescent substance with a long afterglow time that lasts for more than several hours.
Furthermore, if the light-transmitting sintered bodies of the present invention are classified according to the components, the following can be cited: those formed mainly of a compound containing elements with an ionic valence of two except for rare earth elements, rare earth elements and oxygen element as main components.
The compounds containing elements with an ionic valence of two except for rare earth elements, rare earth elements and oxygen element as main components include the following (but as in the above case, the presence of those compounds in the form of light-transmitting sintered body is not known): the above-mentioned bivalent rare earth elements ion activated aluminate-type efficient phosphor, MgY2O4, CaSm2O4, SrYb2O4, BaEu2O4, ZnLa2O4 and other various compounds.
Light-transmitting sintered bodies formed of rare earth elements with an ionic valence of two, aluminum element, and oxygen element as main component or those formed of elements with an ionic valence of two except for the above-mentioned rare earth elements, rare earth elements and oxygen element are preferably made up mainly of compounds containing alkaline rare earth elements, and more preferably oxides.
However, all the light-transmitting sintered bodies according to the present invention are not included in the compounds containing the above-mentioned rare earth elements with an ionic valence of two, aluminum element, oxygen element or the compounds with an ionic valence of two except for rare earth elements, rare earth elements, oxygen element.
The light-transmitting sintered bodies according to the present invention or the compounds having a magnetoplumbite structure, if expressed in a composition formula, include those expressed in xcex1(1)xcex4(1) AlxOy where xcex1 (1) represents at least one element selected from the group consisting of Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and xcex4 (1) represents at least one element selected from the group consisting of Mg, Zn, Mn and where x has a value satisfying 5.5xe2x89xa6x xe2x89xa622, and y has a value satisfying 9.5xe2x89xa6yxe2x89xa638.
Furthermore, the light-transmitting sintered bodies according to the present invention or the compounds containing elements with an ionic valence of two except for rare earth elements, rare earth elements, oxygen element as main components, if expressed in a composition formula, include those expressed in xcex3(2)xcex4(2)AlxOy where xcex3(2), with an ionic valence of two expressed in (II), represents at least one element selected from the group consisting of Ca, Sr, Ba, Eu(II), Sm(II), Yb(II), Dy(II) and xcex4 (2) represents at least one element selected from the group consisting of Mg, Zn, Mn and where x has a value satisfying 5xe2x89xa6xxe2x89xa620, and y has a value satisfying 8.5xe2x89xa6yxe2x89xa634.
Still furthermore, the light-transmitting sintered bodies according to the present invention, if expressed in a different composition formula, include those based on a compound expressed in xcex3(2)AlxOy where xcex3(2), with the ionic valence of two expressed in (II), represents at least one element selected from the group consisting of Ca, Sr, Ba, Eu(II), Sm(II), Yb(II), Dy(II) and where x has a value satisfying 1xe2x89xa6xxe2x89xa624, and y has a value satisfying 2xe2x89xa6yxe2x89xa638.
Furthermore, the light-transmitting sintered bodies according to the present invention or the compounds containing elements with an ionic valence of two except for rare earth elements, rare earth elements, oxygen element as main components, if expressed in a composition formula, include those expressed in xcex3(4)xcex1(1)xOy where xcex1(1) represents at least one element selected from the group consisting of Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu where xcex3(4) represents at least one element selected from the group consisting of Mg, Ca, Sr, Ba, Zn and where x has a value satisfying 1xe2x89xa6xxe2x89xa64, and y has a value satisfying 2xe2x89xa6yxe2x89xa68.
Also, the light-transmitting sintered bodies according to the present invention include those so formulated as to contain metallic ionsxe2x80x94rare earth elements, Mn, Pb, Tl etc.xe2x80x94that can be the luminescent center of the fluorescent substance. In this case, the electric discharge lamps (Xe electric discharge lamp, Ar+Hg electric discharge lamp etc.) as light source for illumination equipment emit ultraviolet rays with a wave-length of not shorter than 100 nm and not longer than 380 nm. To convert the ultraviolet rays into visible rays, it is preferable to make such a light-transmitting sintered body (light-transmitting fluorescent sintered body) that emits fluorescent light under irradiation with ultraviolet rays with a wave-length of not smaller than 100 nm and not larger than 380 nm. The light-transmitting sintered body according to the present invention may be formulated with a long afterglow fluorescent substance with long afterglow efficiency. The long afterglow efficient phosphor will be described later.
The light-transmitting sintered body according to the present invention can be made by the conventional method for making light-transmitting sintered bodies without difficulty. The method comprises the steps of:
Mixing a plurality of pulverized inorganic compounds with a purity of not lower than 99.9%;
Forming into a specific shade the mixture of the pulverized inorganic compounds after the mixing step or, furthermore, after preliminarily calcinating the pulverized inorganic compounds at not lower than 800xc2x0 C. and not higher than 1,800xc2x0 compound, preferably not lower than 1,000xc2x0 C. and not higher than 1,600xc2x0 C. following the mixing step;
After-calcinating(sintering) the formed body obtained after forming at not lower than 1,600xc2x0 C. and not higher than 2,000xc2x0 C., preferably not lower than 1,700xc2x0 C. and not higher than 1,900xc2x0 C. Other methods than that may be used.
The above temperature range is set that way because the melting point of the compounds forming the light-transmitting sintered body according to the present invention is not lower than 1500xc2x0 C. and not higher than 2,200xc2x0 C. In other words, it is desired that the temperature range for preliminary calcination is such that the pulverized inorganic compound materials become a mixture of chemically active compounds. That temperature range is not lower than 800xc2x0 C. and not higher than 1,800xc2x0 C., preferably not lower than 1,000xc2x0 C. and not higher than 1,600xc2x0 C. indicated above for preliminary calcination.
On the other hand, it is desirable that after-calcination is performed at a temperature not exceeding but close to the melting point in such a way that no impurities creep in and non-stoichiometric composition is not caused. For this reason, the temperature range is set at not lower than 1,600xc2x0 C. and not higher than 2,000xc2x0 C., preferably not lower than 1,700xc2x0 C. and not higher than 1,900xc2x0 C.
The atmosphere for the above-mentioned calcinations is selected mainly from the atmospheric air, nitrogen atmosphere, inert gas atmosphere, reduction atmosphere (atmosphere containing hydrogen gas, carbon monoxide atmosphere or vacuum atmosphere), these atmospheres being either reduced pressure atmospheres or vacuum atmospheres.
The light-emitting tube according to the present invention is formed using the above-mentioned light-transmitting sintered body at least in part. And the electric discharge lamp is constructed using that light-emitting tube.